The invention relates generally to infusion pumps and methods of pumping infusion type fluids for intravenous, parenteral, enteral, antibiotic and other medical uses. More specifically, the invention relates to an apparatus and method for safely pumping infusion fluids into a patient when the height of the infusion pump relative to the patient may vary.
Infusion fluids normally are supplied to a patient from a flexible reservoir bag through a long, flexible tube. Sufficient fluid pressure is created by gravity acting on the fluid in the bag and tube to feed the fluid at an acceptable pressure and rate. This was traditionally accomplished in hospital applications by suspending the reservoir bag from a pole. Because the height of the suspended bag relative to the patient varied little regardless of whether the patient was resting in bed or standing, the pressure of the fluid on the patient was not susceptible to significant gravitational, inertial or hydraulic effects which substantial variations in height would create.
As an alternative to passive, gravity-feed infusion, infusion pumps which mechanically induce pressure on the fluid in the bag or other reservoir have been developed. For example, Fletcher et al. U.S. Pat. No. 4,033,479 discloses an apparatus to administer intravenous solutions during space flight by mechanically pressing on the solution-containing bag with a constant pressure. Another example is the device shown in Cherkin U.S. Pat. No. 2,761,445 which squeezes the bag by use of a platform which is moved by a variable speed motor. A more sophisticated, programmable infusion pump is the subject of allowed patent application U.S. Ser. No. 969,981, entitled Method for Pumping Fluid From A Flexible, Variable Geometry Reservoir, filed Nov. 2, 1992. The entire disclosure of U.S. Ser. No. 969,981 is incorporated by reference herein.
These infusion pumps generally only control the pressure of the fluid in the reservoir or the volume of the reservoir and do not address the pressure of the fluid at the point it is received by the patient. Typical infusion tubing can be four feet long or longer and, therefore, will allow pumps to be placed four feet above or below the patient. Moreover, the height of the pump and associated reservoir relative to the patient may vary during use.
If an infusion pump is located above the patient, the fluid will be under substantially more pressure at the point of infusion into the patient than it is in the reservoir. This "free flow" scenario would not be detected by the pumps described above, which have no means to control a greater than desired flow of fluid which may result from such a situation. Indeed, in the case of the Fletcher et al. device, additional mechanically induced pressure is added by the device to whatever pressures are being experienced by the patient as a result of "free flow."
If the pump is located below the patient, the pump will have to overcome substantial back pressure of the column of fluid in the tube. Potentially, a patient in a back pressure situation will lose a significant amount of the solution feed rate and, in extreme cases, a patient's blood could back-flow into the tubing or reservoir. This "blood back-up" scenario might not be detected or avoided in the prior art pumps because the pumps operate independently of the fluid pressure at the point it enters the patient. As mentioned above, those prior art devices do not respond to large discrepancies between the pressure of the fluid in the bag and its pressure at the point it enters the patient, even though such pressure may vary significantly as the relative height of the pump to the patient changes.
It is an object of the present invention to provide a system and a method to control the infusion of intravenous fluid into a patient from an infusion pump.
It is another object of the present invention to provide a system and a method to control the infusion of intravenous fluid into a patient from an infusion pump independent of pump height relative to the patient and without making contact with the intravenous fluid.
It is a further object of the present invention to provide a system and a method to control the infusion of intravenous fluids into a patient independent of the height of the pump relative to the patient by applying external pressure to the flexible, disposable tube which supplies the fluid from the pump to the patient.
It is yet another object of the present invention to provide a safety feature and method to make infusion pumps less susceptible to undesirable "free-flow" and "blood back-flow" situations.
It is yet a further object of the present invention to provide a system and method to increase the safety of infusion pumps designed for use by patients outside the close supervision provided in a hospital.
Other and additional objects are apparent from the following discussion of the invention and its preferred embodiment.